The present invention relates to a variable rate transmission method in radio communications, and more particularly to a variable rate transmission method and equipment for implementing it, which are applicable to direct spreading code division multiple access (DS-CDMA) in mobile communications.
In DS-CDMA, information data undergoes narrow-band carrier modulation (such as binary phase shift keying or quadrature phase shift keying), followed by spreading using a higher rate binary spreading code sequence, and by transmission. On a receiving side, the received signal is-multiplied by the same binary spreading code sequence as that used in the transmission to acquire the original narrow-band modulated signal, followed by demodulation to the original transmitted data.
In actual communications, however, the information rate is not always kept constant. For example, although voice communications is carried out at a rate of about 8 kbps, pauses in which no voice signal is present takes place frequently, and lowering the information rate in the pauses little degrades the voice quality. It is very important for the CDMA to reduce transmission power during a low information rate to minimize interference on other channels.
This is because the magnitude of interference determines the communication quality. Thus, implementation of the variable rate transmission method is important in the CDMA.
As one of the variable rate methods, intermittent transmission is known. It carries out, during a maximum information rate, continuous transmission, but reduces, at lower rates, the average transmission rate down to an information rate by decreasing the ratio of transmission intervals with maintaining the instantaneous transmission rate at the maximum, thereby trying to reduce the interference amount.
As for the intermittent transmission, refer to the following literature.
Reference 1: R. Padovani, R., xe2x80x9cReverse link performance of IS-95 based cellular systemsxe2x80x9d, IEEE Personal Communications, pp. 28-34, 3rd Quarter, 1994.
Reference 2: Y. Okumura and F. Adachi, xe2x80x9cVariable rate data transmission with blind rate detection for coherent DS-CDMA mobile radioxe2x80x9d, IEE Electron Lett. vol. 32, pp. 1865-1866, September 1996.
As another variable rate transmission method in the CDMA, continuous transmission is known which not only varies the instantaneous transmission rate of radio in response to variations in the information rate, but also controls the transmission power in response to the transmission rate.
The average interference amount can also be reduced in the continuous transmission as in the intermittent transmission because the transmission power is varied (in inverse proportion to) the transmission rate in the continuous transmission.
In the CDMA technology, the transmission power control is essential which controls the transmission power so that a received SIR (signal to interference ratio) measured on the receiving side matches a predetermined target SIR in response to results obtained by comparing the two values (refer to Japanese patent application laid-open No. 8-162972/1996 applied by the assignee of the present invention, for example). In this technique, the SIR of a received signal is measured slot by slot and compared with the target SIR, the slot being defined as a section in a received signal sandwiched by two successive pilot signals of a known pattern which are transmitted periodically. Then, a transmission control command is generated in response to the compared result, and is transmitted to the transmitting side to be reflected on the transmission power control. The transmission period of the transmission power control command is a slot interval, that is, the measuring interval.
The transmission power control cannot maintain constant reception quality if it uses the same target SIR for different rates when varying the transmission power in response to the transmission rate. Therefore, the conventional transmission power control that employs the target SIR cannot be applied without change to a transmitted signal whose transmission power is controlled in response to the transmission rate.
An object of the present invention is to provide a transmitting method and receiving method and equipment for implementing the variable rate transmission method employing the foregoing continuous transmission scheme.
Another object of the present invention is to implement the transmission power control capable of achieving constant receiving quality on the receiving side regardless of rate variations when the transmission power is varied in response to the transmission rate (in inverse proportion to it, for example).
In order to accomplish the objects aforementioned, according to the invention claimed in claim 1 a variable rate transmission method comprising the steps of:
preparing a plurality of orthogonal codes whose lengths differ from each other and whose information rates are at least twice a maximum information rate, for one communication with one receiving side in which a rate of information to be transmitted changes, before the communication starts;
selecting, during the communication, in accordance with the changing rate of information to be transmitted, one of the prepared orthogonal codes;
multiplying a signal to be transmitted including the information by the selected orthogonal code; and
transmitting the signal to be transmitted which has been multiplied by the selected orthogonal code, without increasing transmission amount for transmitting information about the selected orthogonal code, during the communication,
wherein each of the plurality of orthogonal codes corresponds to each value that the rate of information to be transmitted assumes.
The method further includes continuously transmitting the signal which has been multiplexed by the selected orthogonal code, even if the selected orthogonal code has changed.
According to the invention as claimed in claim 2, in the variable rate transmission method as claimed in claim 1, where the step of preparing the orthogonal codes prepares orthogonal codes obtained by successively generating, using lower degree matrices under a predetermined rule, higher degree (2Nxc3x972N elements, where N is an integer equal to or greater than one) matrices with their row vectors orthogonal to each other, and by selecting one of row vectors of one of the matrices with a degree varying in accordance with each value that the rate of information to be transmitted assumes.
According to the invention as claimed in claim 3, in the variable rate transmission method as claimed in claim 2, where the step of preparing orthogonal codes prepares the orthogonal codes such that the orthogonal codes no not include both an orthogonal code corresponding to one of row vectors of a 2kxc3x972k element matrix (k is an integer less than N), and an orthogonal code corresponding to any one of row vectors of any one of 2Jxc3x972j element matrices (j is an integer greater than k) which includes as its sub-vector, the one of the row vectors of the 2kxc3x972k element matrix or a row vector obtained by inverting the one of the row vectors of the 2kxc3x972k element matrix.
According to the invention claimed in claim 4, in the variable rate transmission method as claimed in claim 1, the signal is further multiplied by a spreading code sequence to be spectrum spread, and is transmitted at transmission power corresponding to the rate of information to be transmitted.
According to the invention as claimed in claim 5, the variable rate transmission method as claimed in claim 4, further comprises the steps of:
inserting pilot symbols of a known pattern periodically into data symbols corresponding to the information to be transmitted; and
varying the rate on a frame by frame basis, the frame consisting of a plurality of slots defined by the pilot symbols.
According to the invention as claimed in claim 6, the variable rate transmission method as claimed in claim 5, further comprises the step of controlling the transmission power on a slot by slot basis in response to a transmission power control command sent from a receiving side.
According to the invention as claimed in claim 7, the variable rate transmission method as claimed in claim 6, further comprises the step of transmitting, in a slot immediately after a rate change, the pilot symbols at power corresponding to the rate before the rate change.
According to the invention as claimed in claim 8, the variable rate transmission method as claimed in claim 6, further comprises the step of suspending the transmission power control by the transmission power control command that is associated with at least one of slots immediately after a rate change.
According to the invention as claimed in claim 9, in the variable rate transmission method as claimed in claim 8, a number of slots with which the transmission power control is suspended is determined in response to transmission quality.
According to the invention as claimed in claim 10, in the variable rate transmission method as claimed in claim 5, the pilot symbols are transmitted at a same rate as that of said frame.
According to the invention as claimed in claim 11, in the variable rate transmission method as claimed in claim 5, the pilot symbols are transmitted at a fixed rate.
According to the invention as claimed in claim 12, a variable rate receiving method for receiving a signal transmitted by the variable rate transmission method as claimed in claim 1, comprises the steps of:
generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes, and calculating correlations between the sampled sequence of the received signal and the plurality of orthogonal codes with different lengths;
deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations; and
demodulating the received signal by multiplying the sampled sequence of the received signal by the orthogonal code that gives the maximum correlation value.
According to the invention as claimed in claim 13, a receiving method for receiving a signal transmitted by the variable rate transmission method as claimed in claim 6, comprises the steps of:
generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
calculating correlations between the sampled sequence of the received signal and the plurality of orthogonal codes with different lengths;
deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
demodulating the received signal by multiplying the sampled sequence of the received signal by the orthogonal code that gives the maximum correlation value, and measuring a received SIR for each slot of the received signal;
correcting the received SIR according to a rate of the orthogonal code decided by the step of deciding;
comparing the corrected received SIR with a target SIR; and
generating a transmission power control command in response to a result of the comparing.
According to the invention as claimed in claim 14, in the receiving method as claimed in claim 13, demodulation of the received signal is carried out slot by slot.
According to the invention as claimed in claim 15, a receiving method for receiving a signal transmitted by the variable rate transmission method as claimed in claim 7 comprises the steps of:
generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
calculating correlations between the sampled sequence of the received signal and the plurality of orthogonal codes with different lengths;
deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
demodulating the received signal by multiplying the sampled sequence of the received signal by the orthogonal code that gives the maximum correlation value;
measuring a received SIR of the pilot symbols for a slot immediately after a rate change, and a received SIR for each of other slots;
correcting the received SIR for each of other slots according to a rate decided by the decision of the orthogonal code;
correcting the received SIR of the pilot symbols according to a rate before the rate change;
comparing the corrected received SIR with a target SIR; and
generating a transmission power control command in response to a result of the comparing.
According to the invention as claimed in claim 16, a receiving method for receiving a signal transmitted by the variable rate transmission method as claimed in claim 11, comprises the steps of:
generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
calculating correlations between the sampled sequence of the received signal and the plurality of orthogonal codes with different lengths;
deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
demodulating the received signal by multiplying the sampled sequence of the received signal by the orthogonal code that gives the maximum correlation value;
measuring a received SIR of the pilot symbols at the fixed rate;
correcting the received SIR according to a rate decided by the decision of the orthogonal code;
comparing the corrected received SIR with a target SIR; and
generating a transmission power control command in response to a result of the comparing.
According to the invention claimed in claim 17, a variable rate transmitter comprising:
an orthogonal code generator for preparing a plurality of orthogonal codes whose lengths differ from each other and whose information rates are at least twice a maximum information rate, for one communication with one receiving side in which a rate of information to be transmitted changes, before the communication starts, and generating, during the communication, in accordance with the changing rate of information to be transmitted, one of the prepared orthogonal codes;
a multiplier for multiplying a signal to be transmitted including the information by the orthogonal code fed from the orthogonal code generator; and
a transmitter for transmitting the signal to be transmitted which has been multiplied by the orthogonal code fed from the orthogonal code generator, without increasing transmission amount for transmitting information about the orthogonal code fed from the orthogonal code generator, during the communication,
wherein each of the plurality of orthogonal codes corresponds to each value that the rate of information to be transmitted assumes.
The transmitter further includes means for continuously transmitting the signal which has been multiplexed by the orthogonal code fed from the orthogonal code generator, even if the orthogonal code fed from the orthogonal code generator has changed.
According to the invention claimed in claim 18, in the variable rate transmitter as claimed in claim 17, the orthogonal code generator prepares orthogonal codes obtained by successively generating, using lower degree matrices under a predetermined rule, higher degree (2Nxc3x972N elements, where N is an integer equal to or greater than one) matrices with their row vectors orthogonal to each other, and by selecting one of row vectors of one of the matrices with a degree varying in accordance with each value that the rate of information to be transmitted assumes.
According to the invention claimed in claim 19, variable rate transmitter as claimed in claim 18, where the orthogonal code generator prepares orthogonal codes such that the orthogonal codes do not include both a orthogonal code corresponding to one of row vectors of a 2kxc3x972k element matrix. (k is an integer less than N), and an orthogonal code corresponding to any one of row vectors of any one of 2jxc3x972j element matrices. (j is an integer greater than k), which includes as its sub-vector, the one of the row vectors of the 2k xc3x972k element matrix or a row vector obtained by inverting the one of the row vectors of the 2kxc3x972k element matrix.
According to the invention as claimed in claim 20, the variable rate transmitter as claimed in claim 17, further comprises:
a spreading sequence generator for generating a spreading code sequence for spectrum spreading;
a multiplier for multiplying the signal by the spreading code sequence fed from the spreading sequence generator; and
a transmitter for varying transmission power in response to the rate of information to be transmitted.
According to the invention as claimed in claim 21, the variable rate transmitter as claimed in claim 20, further comprises a pilot symbol generator for generating pilot symbols of a known pattern periodically, wherein the pilot symbols are inserted into data symbols corresponding to the information to be transmitted, and the rate is varied on a frame by frame basis, the frame consisting of a plurality of slots defined by the pilot symbols.
According to the invention as claimed in claim 22, the variable rate transmitter as claimed in claim 21, further comprises a transmission power controller for controlling the transmission power on a slot by slot basis in response to a transmission power control command sent from a receiving side.
According to the invention as claimed in claim 23, in the variable rate transmitter as claimed in claim 22, the pilot symbols are transmitted, in a slot immediately after a rate change, at power corresponding to the rate before the rate change.
According to the invention as claimed in claim 24, in the variable rate transmitter as claimed in claim 21, where the pilot symbols are transmitted at a same rate as that of the frame.
According to the invention as claimed in claim 25, in the variable rate transmitter as claimed in claim 21, where the pilot symbols are transmitted at a fixed rate.
According to the invention as claimed in claim 26, in the variable rate transmitter as claimed in claim 22, the transmission power control by the transmission power control command that is associated with at least one of slots immediately after a rate change is suspended.
According to the invention as claimed in claim 27, in the variable rate transmitter as claimed in claim 26, a number of slots with which the transmission power control is suspended is determined in response to transmission quality.
According to the invention as claimed in claim 28, a variable rate receiver for receiving a signal transmitted by the variable rate transmission method as claimed in claim 1 comprises:
a sampler for generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
a correlator for calculating correlations between the sampled sequence of the received signal from the sampler and the plurality of orthogonal codes with different lengths;
an orthogonal code decision block for deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
an orthogonal code generator for generating the orthogonal code decided by the orthogonal code decision block; and
a multiplier for multiplying the sampled sequence of the received signal by the orthogonal code from the orthogonal code generator to demodulate the received signal.
According to the invention as claimed in claim 29, a receiver for receiving a signal transmitted by the variable rate transmission method as claimed in claim 6 comprises:
a sampler for generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
a correlator for calculating correlations between the sampled sequence of the received signal and the plurality of orthogonal codes with different lengths;
an orthogonal code decision block for deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
an orthogonal code generator for generating the orthogonal code decided by the orthogonal code decision block;
a multiplier for multiplying the sampled sequence of the received signal by the orthogonal code from the orthogonal code generator;
a received SIR for measuring a received SIR for each slot of the received signal;
a correcting block for correcting the received SIR according to a rate of the orthogonal code decided; and
a comparator for comparing the corrected received SIR with a target SIR,
wherein a transmission power control command is generated in response to a result of the comparing.
According to the invention as claimed in claim 30, in the receiver as claimed in claim 29, demodulation of the received signal is carried out slot by slot.
According to the invention as claimed in claim 31, a receiver for receiving a signal transmitted by the variable rate transmission method as claimed in claim 7 comprises:
a sampler for generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
a correlator for calculating correlations between the sampled sequence of the received signal from the sampler and the plurality of orthogonal codes with different lengths;
an orthogonal code decision block for deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
an orthogonal code generator for generating the orthogonal code decided by the orthogonal code decision block;
a multiplier for multiplying the sampled sequence of the received signal by the orthogonal code from the orthogonal code generator;
a received SIR measuring block for measuring a received SIR of the pilot symbols for a slot immediately after a rate change, and a received SIR for each of other slots;
a correcting block for correcting the received SIR for each of other slots according to a rate decided by the decision of the orthogonal code, and for correcting the received SIR of the pilot symbols according to a rate before the rate change; and
a comparator for comparing the corrected received SIR with a target SIR,
wherein a transmission power control command is generated in response to a result of the comparing.
According to the invention as claimed in claim 32, a receiver for receiving a signal transmitted by the variable rate transmission method as claimed in claim 11 comprises:
a sampler for generating a sampled sequence of a received signal by sampling the received signal at a rate of one of the orthogonal codes;
a correlator for calculating correlations between the sampled sequence of the received signal and the plurality of orthogonal codes with different lengths;
an orthogonal code decision block for deciding an orthogonal code that gives a maximum correlation by comparing correlation values obtained as a result of the calculation of the correlations;
a multiplier for multiplying the sampled sequence of the received signal by the orthogonal code that gives the maximum correlation value;
a received SIR measuring block for measuring a received SIR of the pilot symbols at the fixed rate;
a correcting block for correcting the received SIR according to a rate decided by the decision of the orthogonal code; and
a comparator for comparing the corrected received SIR with a target SIR,
wherein a transmission power control command is generated in response to a result of the comparing.